The investigators are playing down a suggestion by a member of the UN Commisson of Inquiry on Syria that there was evidence of the nerve gas sarin being used by rebels.
Investigator Carla Del Ponte caught UN officials by surprise on Sunday when she said the commission had gathered testimony from casualties and medical staff indicating that rebel forces had used the banned nerve agent sarin, Reuters reports.
In a statement, the commission said it wished to clarify that it had not reached conclusive findings as to the use of chemical weapons in Syria by any parties to the conflict.
Ms Del Ponte gave no details as to when or where sarin may have been used. She was speaking in an interview with Swiss-Italian television.
In comments posted in English on Monday, she repeated the assertion, saying that witness testimony made it appear that some chemical weapons had been used.
President Bashar al-Assad's government and the rebels his forces have been fighting for more than two years accuse each another of carrying out three chemical weapon attacks in March and December, in Aleppo, Damascus and Homs.
US President Barack Obama has warned any confirmed use of chemical weapons by Assad would cross a "red line" and British Prime Minister David Cameron said late last month there was limited but growing evidence the banned arms had been used.
A diplomatic source told Reuters on Monday soil samples from Syria have tested positive at Britain's Porton Down military facility for sarin - though it was not clear where the samples came from.
A Syrian medic working near the Turkish border said his patients also showed signs of exposure to the gas - but only a diluted form, possibly released to scare but not kill them.